Means and method of processing thermionic tubes



W. W. EITEL April 2, 1935.

MEANS AND METHOD OF PROCESSING THERMIONIG TUBES F' iled Sept. 12, 1932INVENTORY v lillmlnllllllltrlllllvlliillfll M W ATTORNEY Patented Apr.2, 1935 "MEANS l i m W.- titel. i nii 'Park to Heinti & Kan 7 Galifi, acorporation of Nevada 1,996,506 AND METHOD. on. PRocEssiNG.

THERMIONIG TUBES I man, Ltd's Qal h assi zi b Sari Francisco;

Applicationl'Septembe-r 12, 1 932, No. g

3 Claims.

My invention relates to means and method of introducing a volatile metalinto a thermionic tube, and more particularly to the processing of suchtubes as use mercury vapor as a conducting medium.

Among the objects of my invention are: To provide a simple and effectivemeans of releasing volatile metal in a thermionic tube; to provide amethod of releasing purified volatile metal in a thermionic tube afterthe tube has been evacuated;

to provide a method of processing thermionic tubes in which mercury isto be used as a conducting medium; and to provide a simple andinexpensive method of processing a mercury arc Other objects of myinvention will be apparent or will be specifically pointed out in thedescription forming a part of this specification, but I do not limitmyself to the embodiment of my invention herein described, as variousforms may be adopted within the scope of the claims.

In the drawing, representing one preferred embodiment of my invention:

Figure 1 is a longitudinal sectional view of a mercury arc rectifiershowing the positioning of a mercury capsule.

Figure 2 is an enlarged view of the capsule. Figure 3 is a sectionshowing a method of preparing a capsule.

In the processing of thermionic tubes, particularly in the degassing ofelements and evacuation to a high degree, it often happens that thepresence of volatile metals later to be used in the tube, prevents theproper evacuation, and almost always lengthens the time required forpumping. It is in many cases desirable to completely pump the tube, andthen insert the volatile metal. Such insertions often requirecomplicated apparatus and costly precautions.

Broadly speaking my invention comprises the insertion into a thermionictube of such volatile metal sealed in a frangible capsule which willremain sealed and inert during the evacuation of the tube but which canbe broken by heat locally applied to the metal.

I prefer to generate this heat by the application of high frequency fromwithout the tube to cause eddy currents in the metal. I also prefer topurify the metal contained in the capsule.

Referring to the figures which show only one specific form of myinvention as applied to a mercury arc rectifier, an envelope l isprovided with a reentrant stem 2 having cathode leads 4 sealed through apinch 5. upwardly into the tube and carry a These cathode leads extendcathode filament 6 which in this instance is a coiled oxidecoatedribbon. An anode 1 is supported from the top of the envelope by an anodelead 9 passing through the envelope at a seal l0.

A frangible capsule H is prepared as shown 5 in Figure 3. A length ofglass tubing I2 is provided with a bulb portion It and is then filledwith mercury i5. This mercury may be purified in any approved mannerandthe bulb portion is then sealed oif from the tubing by a flame Hi to 10form the capsule. Almost any of the common glasses have a thermalexpansion coefficient less than that of mercury and I have found thatlead glass is satisfactory.

The capsule isthen mounted in a frame com- 15 prising a strut ll forminga ring l8 around a capsule seal l9. Capsule support 20 extendsunderneath the capsule and is welded to the strut I l. I prefer to makethe entire frame from nickel wire. 7

The end of the strut ll may then be welded to some portion of the tubeelements, and in this case I have shown it attached to one of thecathode leads 4 near the pinch, with the capsule approaching the sidewall of the tube. 25

o I have found that the tube may be evacuated, baked out, degassed orotherwise heat treated without danger of the capsule liberating itscontents. When desired, at or near the end of the processing, or afterthe tube has been sealed off the pumps, a bombarder, coil 2| may besupplied with high frequency through leads 22 and eddy currentsgenerated by induction into the mercury l5.

These eddy currents cause heating of the mercury inside the capsule andthe capsule cracks. All of the contained metal is expelled by vaporpressure through the crack and the metal. is thereby released into thetube where it can take up its prescribed duty. 7 40 If higher power inthe bombarder coil is used and intense heat generated quickly in themercury, the capsule will burst and the contained material expelled atonce.

I therefore have provided a means of introducing mercury into an arctube after all preliminary processing has been accomplished.

While the description above refers to a mercury arc, I have also beenable to insert other metals such as sodium, potassium, and likematerials, in the same manner. When these metals are used, which aresolid at room temperatures, the eddy currents will first melt them, thenthe container will fracture and the metals will be expelled inliquidform. 55

I claim: I

1. In combination with a thermionic tube envelope, a capsule containinga volatile material, said capsule being flask-shaped and having a mainspherical portion and a restricted neck portion, a. main support wireadapted to be attached at one end to an element within said envelope andhaving the other end shaped to encircle said neck portion, and a bodysupporting wire attached to said main support wire and passing belowsaid spherical portion to provide support therefor.

2. In combination with a thermionic tube envelope, a capsule containinga volatile material, said capsule being flask-shaped and having a mainspherical portion anda restricted neck portion, a main support wireadapted to be attached at one end to an element within said envelope andhaving the other end shaped to encircle said neck portion, and a bodysupporting wire attached to said main support wire and passing belowsaid spherical portion to provide support therefor, said body supportingwire being open circuited.

3. In combination with a thermionic tube envelope, a capsule containinga volatile material, said capsule, being flask-shaped and having a mainspherical portion and a restricted neck portion, a. main support wireadapted to be attached at one end to an element within said envelope andhaving the other end shaped to encircle said 'neck portion, and a bodysupporting wire attached to said main support wire and passing belowsaid spherical portion to provide support therefor, the circle of saidmain support wire being substantially smaller in diameter than thediameter of said spherical portion, and said body supporting wire beingopen circuited.

' WILLIAM W. EITEL.

